The aims of the study are to determine in adipose tissue (1) the effects of norepinephrine (NE), isoprenaline (ISO) and histamine (H) on capillary hydrostatic pressure; (2) the inter-relationship between changes in capillary pressure and rates of glycerol output; and (3) the changes in geometry of the microvasculature during stimulation of the sympathetic nerves. Variations in blood flow and alterations in relative permeability of the capillary wall may influence the rate of outflow of glycerol and free fatty acids (FFA) from adipose tissue. Altered flow patterns during neurohumoral stimulation may also contribute to the regulation of lipolytic output. The present study will attempt to estimate the relative permeability of the capillary wall during infusion of the amines. This might be accomplished by comparing the values for capillary hydrostatic pressure (Pci) with protein osmotic pressures of plasma and tissue fluid during several physiological states. In these experiments, Pci will be measured in isolated, autoperfused omental and mesenteric fat with the method of Pappenheimer and Soto-Rivera. NE, ISO and H will be infused close intra-arterially into the adipose tissue. Measurements will be made of Pci, glycerol output and blood flow. In a separate set of experiments, the vascular bed of mesenteric fat will be filled with a fluorescent silicone elastomer. The pattern of microvasculature will be compared between control preparations and tissues filled during prolonged nerve stimulation. Photographic documentation will provide a permanent record of the changes.